1. Field of the Invention
The present invention relates to the field of seat furniture. It relates particularly to a tilt device for seat furniture, comprising
(a) a base which can be fastened to an underframe of the seat furniture, preferably a chair column, and which serves as a carrier for a seat and a backrest;
(b) an angular backrest carrier with a lower leg and an upper leg, said backrest carrier being rotatably mounted on the base in the middle region of its lower leg by means of a rotary bearing and consisting, at least in its lower leg, of two backrest cheeks arranged parallel to and at a distance from one another;
(c) a seat plate which is supported at least in its front region by the base; and
(d) at least one spring element which is fastened to the base on one side and which on the other side engages on the backrest carrier behind the rotary bearing and exerts an upwardly directed force on the backrest carrier.
Such a tilt device is known, for example, from EP-B1-0,233,974 of the same applicant.
2. Discussion of the Related Art
Two solutions conducive to dynamic sitting have found acceptance:
(1) As a basic version, chairs with a so-called "permanent-contact backrest", that is to say with a backrest mechanism which generates a specific countermoment, in order to compensate the variable leaning moment of the chair user by means of the tilting range of the backrest. The range of countermoments generated can at the same time, if appropriate, be adjusted to the individual weight of the user's upper body.
(2) As a sophisticated version, chairs or armchairs with a so-called "simultaneous" or "synchronous" mechanism. In this mechanism, the seat too--coupled with the permanent-contact backrest--varies its tilt in a specific ratio. Especially when the tilting ranges of the backrest are relatively wide, this simultaneous or synchronous change of the seat tilt is a necessary measure, in order, among other things, to counteract the forward displacement of the buttocks which occurs as a result of the leaning moment.
In the publication mentioned in the introduction, although a chair mechanism allowing the two above-explained possibilities of variation is described, nevertheless this known chair mechanism has essentially the following disadvantage:
The basic elements of the mechanism (housing, springing, locking, etc.) are designed for the complicated simultaneous mechanism. The constructional outlay and production costs are therefore considerable, because, in principle, a simultaneous mechanism has to be "scaled down", in order to obtain a simpler permanent-contact mechanism. At the same time, the relatively expensive housing made of cast metal or fiber-reinforced plastic, the complicated selectively usable locking for retained positions and other special designs of the mechanism are preserved.